Wireless technology has been broadly adopted for network systems, broadcasting systems, positioning systems, mobile interconnection systems, and communication systems. One of the most important aspects of wireless technology is the use of a wireless receiver for receiving wireless signals. In modern wireless technology, a wireless receiver receives wireless signals with an antenna, amplifies the received signal, mixes the amplified signal with local oscillation signal(s), filters the mixed signal (e.g., by low-pass and/or band-pass filter(s)), and performs analog-to-digital conversion to convert the filtered signal to a digital signal, such that information, data, audio/video streams, packets, and/or messages carried in the original wireless signal can be retrieved by digitally processing the digital signal.
While amplifying the received signal, factors such as noise, bandwidth, gain control ability, and linearity are of main concern. Amplification techniques resulting in low noise, high linearity, and broad bandwidth are demanded to provide good noise figures, low signal distortion, and support of modern modulation schemes (e.g., spread spectrum and/or frequency multiplexing). To fully utilize the dynamic range of analog-to-digital conversion, fine gain control is also required. Magnitude of the received signal varies greatly due to various factors, e.g., deviation of wireless propagation environment/channel and/or distance variation between wireless signal source and the receiver. Different magnitudes of the received signal need to be amplified with different gain, such that magnitude of the amplified signal can match the full dynamic range of the analog-to-digital conversion.
For gain control, a common prior art amplification technique is implemented by two stages of amplifiers; a received signal is first amplified by a low-noise amplifier (LNA), and is then amplified by a variable-gain amplifier (VGA). In the prior art, the low-noise amplifier often implements a step gain control of coarse gain tuning, and the variable-gain amplifier implements a fine gain control. With the step gain control of the LNA, the gain of the LNA is selected from a finite number of different gain levels, so that the gain cannot be fine-tuned to any arbitrary value between any two adjacent gain levels. Consequently, an additional VGA of fine gain control is adopted to fill gaps between the gain levels of the LNA. However, such two stage amplifying architecture occupies a larger physical layout area, consumes more current and power, and also suffers higher noise since more active and/or passive elements are required to implement the amplifying architecture.